At 35ss I would usually run between 3 and 5, they are really cheap and work really well, if you need to get objectives with them I say the more the merrier.
Bete is good, not so sure for novice player (but I started using her when I was a novice so do what you want, you will just have a bit more of a learning curve). You just ned to pay attention to when you get her to come out (when they kill you as she can then activate without retaliation most of the time) and keep a 10 of anything in your hand and she is unkillable. The threat of Bete can also play in your opponents mind too.
Purchases wise I think you would be best off getting the 2 packs of dogs along with Bete, I have found a Belle and a few Necropunks also work nicely with the good doctor and you can definitely get a good swarm going backed up by some heavy hitters